(1) Field of the Invention
The present invention generally relates to a noise-riding video signal threshold generation apparatus and method.
(2) Description of the Prior Art
Electronic warfare receivers, such as crystal video receivers, are used to detect radio frequency (RF) energy in the environment. Typically, the RF energy is collected by an antenna, amplified and then fed into the receiver wherein it is routed to a video detector. The video detector converts the RF energy to a video signal that has a level that is proportionate to the RF signal strength. The video signal is amplified and processed by the receiver to alert the operator of the presence of any RF energy in the environment. Detection of the video is typically accomplished by using a comparator to determine if the video signal exceeds a set threshold. The threshold level is critical to proper operation of the receiver. A threshold set too high degrades the receiver's sensitivity, and the receiver is unable to process weaker signals. On the other hand, if the threshold is set too low, the system noise will exceed the threshold causing the receiver to produce false alarms. Due to temperature changes, noise levels can fluctuate in the system. If a fixed threshold is used, the changing noise levels can produce false alarms or can desensitize the receiver.
Many prior art systems utilize analog systems to filter, invert and rectify the incoming RF signal to separate the noise component from the video signal and generate a video threshold. A review of the prior art reveals several references that disclose a variety of circuits and systems for adaptively generating a video signal threshold.
Phipps et al., U.S. Pat. No. 4,274,095 discloses a radar video converter that uses a computer interface module to select from a plurality of threshold levels for use in detecting radar signals corresponding to targets in a particular radar environment.
Cantwell et al., U.S. Pat. No. 5,091,729 discloses an adaptive threshold detector system that adaptively uses three threshold criteria to detect weak and strong valid signals. The system uses an integrating sum of the detected signal envelope as detection criteria to distinguish between weak and strong signals and to adjust the system detection criteria accordingly.
Lee, U.S. Pat. No. 5,254,999 discloses a video signal processor for a radar system that comprises an A/D converting circuit that converts the radar signals into digital signals, and a cell averaging circuit. The cell averaging circuit adaptively sets a threshold value for determining whether a signal is target data or not. This patent refers to this technique of adaptively setting the threshold value as cell averaging.
Boria, U.S. Pat. No. 6,433,730 discloses a radar receiver that comprises a noise riding threshold circuit that comprises high frequency components of the noise and video signal to produce noise riding threshold voltage.
Based on the aforesaid prior art references, a need still exists for an improved apparatus that adaptively generates video signal thresholds.